1. Field of the Invention
The present invention relates to a hydrostatic transmission, and more particularly to a transmission having a hydrostatic power unit comprising a pump having a pump shaft and a motor having a motor shaft, the pump and motor shafts extending parallel to each other, the hydrostatic pump unit being mounted on a transmission casing which houses a speed reducer mechanism.
2. Description of the Relevant Art
Some working vehicles such as riding-type lawn mowers, tractors, etc. employ a transmission having a hydrostatic power unit comprising a pump having a pump shaft and a motor having a motor shaft, the pump and motor shafts extending parallel to each other.
U.S. Pat. No. 4,862,767 discloses a hydrostatic transaxle having a casing to which a hydrostatic power unit is coupled. The casing defines therein a common or single chamber in which bevel gears of an input shaft and a pump shaft are held in mesh with each other, and parallel gears of a speed reducer mechanism and a motor shaft are also held in mesh with each other. The speed reducer mechanism requires three parallel shafts, i.e., the pump shaft, the motor shaft, and an axle.
With the conventional design, the bevel gears of the input shaft and the pump shaft are held in mesh with each other, and the parallel gears of the speed reducer mechanism and the motor shaft are also held in mesh with each other in the common chamber defined in the casing. It has been necessary for a reservoir tank of the hydrostatic power unit to be separate from the casing. Therefore, there has been a limitation on efforts to reduce the size of the casing and the entire hydrostatic transaxle.
Another problem that has limited the reduction of the size is that the speed reducer mechanism is composed of three shafts.
The present invention has been made in order to effectively solve the above problems of the conventional transaxle or transmission with a hydrostatic power unit.